Circular saw having an improved tooth geometry and method of making the same

ABSTRACT

A cup-shaped wheel having an abrasive rim is employed to grind the teeth of a circular saw to an improved contour. Only point or edge contact takes place between the abrasive rim and the tooth. This technique is preferably utilized in conjunction with triple-chip type circular saws of the sort used to cut metals such as steel. The contour imparted to the cutting surface of the tooth comprises a section of an elliptical cylinder and exhibits improved steel cutting characteristics when compared to prior art multi-faceted saw teeth. Since only edge contact takes place between the abrasive rim and the tooth, the wheel is essentially self-dressing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This invention is a continuation-in-part and represents an improvementover the invention described in my copending application entitled "ACircular Saw Having Teeth With An Improved Metal Breaking Geometry,"U.S. application Ser. No. 587,504 filed June 16, 1975 now U.S. Pat. No.4,012,820, the entire disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for grinding the teeth of a circularsaw blade to an improved contour and further relates to the saw bladeitself as generated by said method.

2. Description of the Prior Art

Circular saw blades and methods and apparatus for finishing the teeththereof are quite common. Circular saw teeth with carbide inserts,initially having a cylindrical or spherical shape are known to those ofordinary skill in the art. For example, Goehle, U.S. Pat. No. 2,675,603discloses the use of a cylindrical carbide element as a tooth in thecontext of a composite circular saw. While the insert is cylindrical inshape, it is eventually ground and faced so as to have a conventionalworking surface. Kolesch, U.S. Pat. No. 3,537,491 and Tyler, U.S. Pat.No. 3,788,182 both disclose the use of spherical carbide ball insertsadapted for use in other circular saws. However, as in the case ofGoehle, the spheres are subsequently faced and the remaining roundedsection of the sphere is not in actuality the working surface. Lewis,U.S. Pat. No. 485,503, Bruestle et al, U.S. Pat. No. 2,860,863 andLaVelle, U.S. Pat. No. 3,380,497 all disclose prior art circular sawshaving a rounded profile when seen from either the front or the back ofthe tooth. However, the working surface is neither cylindrical, conical,elliptical or spherical. Osgood, U.S. Pat. No. 238,521 and Pioche, U.S.Pat. No. 1,334,633 likewise disclose saws in which the side view profileof the tooth is rounded or cylindrical in some aspects but wherein theworking surface is neither spherical, conical, cylindrical orelliptical.

The problem encountered with old-fashioned carbide tooth saws istwo-fold. One of the problems is that the carbide insert is hard andbrittle and cannot take interrupted cutting. During interrupted cuttingthe shock loading on the teeth is so great that the teeth willfrequently break. The second problem associated with conventionalcarbide insert saws is that carbide has an affinity for many metals thatit cuts. Frequently, a metal chip will get stuck on the face of thecarbide insert or in the gullet thereunder. According to the prior artmethods of cutting, it was often necessary to get rid of this excessmetal by means of an air blast or brushes. Unfortunately, thesetechniques were not always satisfactory and resulted in great bladedeterioration.

Recently, a saw blade having an improved metal cutting geometry wasdisclosed in U.S. Pat. Nos. 3,576,061 and 3,619,880 to Pahlitzsch. Thistype of saw blade is often referred to as the "German" geometry.According to those inventions, an improved cutting characteristic couldbe achieved by slightly beveling the top face of the tooth down towardthe side of the tooth. This technique is similar to the technique of"breaking the corners" in order to prolong saw blade life. While thesaws disclosed in U.S. Pat. Nos. 3,576,061 and 3,619,880 do display someimproved cutting characteristics, they are nevertheless difficult tomanufacture because they require several different grinding steps inorder to achieve a satisfactory geometry. What was desired in thiscontext was a saw blade that exhibited cutting characteristics betterthan those disclosed in U.S. Pat. Nos. 3,576,061 and 3,619,880 and whichwere easier to grind and regrind. The following patents are also of notein that they describe relevant structures: Aber, U.S. Pat. No.2,344,954; Horth, U.S. Pat. No. 2,381,540; Soderstrom, U.S. Pat. No.3,878,747; Haycock, U.S. Pat. No. 2,546,503; Kaiser, U.S. Pat. No.3,434,190; Maurer, U.S. Pat. No. 2,831,240 and Shephard, U.S. Pat. No.2,891,300.

A saw blade having characteristics better than those ascribed to theGerman Geometry is described in my copending application Ser. No.587,504 filed June 16, 1975 now U.S. Pat. No. 4,012,820. It wasdiscovered that an improved working surface can be formed by grinding aportion of the face of the tooth to a continuously curved contour. Sawblades produced with teeth having a working surface with a continuouslycurved contour exhibited superior steel cutting characteristics and wererelatively easy to grind and regrind. FIG. 4a of Ser. No. 587,504illustrates a plunge grinding technique for producing a continuouslycurved contour. FIG. 4b on the other hand, illustrates a grindingtechnique similar to that further disclosed herein. It was found thatthe machinery necessary to produce that type of saw blade had certainundesirable limitations. Accoringly, it is necessary to describe thelimitations of the prior art saw grinding equipment in order toappreciate the full value of the present invention.

The practice of grinding circular saws with abrasive wheels is known tothose of ordinary skill in the art. Grinding equipment is made, forexample, by the Vollmer Corporation of Dornhan, West Germany, andothers. One of the major problems associated with conventional prior artcarbide tipped steel cutting circular saws is that they cut slowly andwear out quickly. This difficulty was greatly reduced by the discoverythat if the top of the face of the saw teeth are specially shaped tohave a more negative rake angle relative to the rake of the rest of thetooth face, then efficiency was greatly improved. The special shapingtypically involved multiple grinding operations in which several flatfacets were formed in the top of the carbide tip. While the new shapewas superior to the old shape, it was nevertheless time consuming togrind due to its multi-faceted contour. A description of this prior artshape may be found in an article by Pahlitzsch and Willemeit whichappeared in Volume 58, Issue 4 of Werkstattstechneik (1968).

The saw blade described in U.S. Pat. No. 4,012,820 was discovered to besuperior in many characteristics to the saw blade generated by the"German" Geometry and disclosed in the patents to Pahlitzsch, U.S. Pat.Nos. 3,576,061 and 3,619,880. A device to automatically and efficientlyproduce the Nowak saw blades was thereafter invented by Horst VonArnauld and Daniel J. Murphy. A description of the Von Arnauld andMurphy invention may be found in pending U.S. application Ser. No.540,449 filed Jan. 13, 1975 now U.S. Pat. No. 3,964,349 and entitled"Method and Apparatus for Grinding the Teeth of a Circular Saw to anImproved Contour." The Von Arnauld and Murphy invention is directedtoward the automatic machinery which grinds the circular saw teeth. Theautomatic apparatus and method comprehended a cup-shaped grinding wheelhaving an abrasive inner rim which is automatically brought intogrinding contact with a tooth of a circular saw. A working (i.e.cutting) surface having a continuously curved contour is therebygenerated. The working surface is further characterized in that ittypically has a more negative average rake angle than the remainingportion of the face of the tooth. The invention further comprehends theuse of a programmed electronic unit which automatically controls therelative movements of the grinding wheel and the saw blade during thegrinding operation. According to the Von Arnauld/Murphy invention abroad section of the abrasive inner rim of the cup-shaped grinding wheelcomes into substantially simultaneous contact with the face of the sawtooth. The grinding wheel plunges into the face of the tooth and remainsthere for as long as necessary to effectuate the necessary grinding.After the tooth is ground the grinding wheel is subsequently retractedand the new tooth is indexed into grinding position. One majordifficulty experienced with the Von Arnauld/Murphy invention is that thegrinding wheels were subjected to a great deal of wear. Since the samepart of the grinding wheel always came into contact with the face of thesaw teeth, the grinding wheel itself eventually took on thecharacteristic contour of the tooth to be ground. Accordingly,subsequent teeth ground with the same grinding wheel often assumed thecharacteristics of the grinding wheel itself and as the grinding wheelbecame progressively worn the contour imparted to the teethprogressively deteriorated. In addition, while the automatic method andapparatus invented by Von Arnauld and Murphy made it possible to grindteeth more efficiently, there were still some time limitations whichdecreased the overall speed of the machinery. Accordingly, new meanswere sought to improve upon the previous method and apparatus.

In addition to the foregoing prior art the following patents appear todisclose relevant structure and methodology: Armstrong, U.S. Pat. No.1,771,602; Markhe, U.S. Pat. No. 2,874,517; Segal, U.S. Pat. No.2,958,240; English, U.S. Pat. No. 3,304,810; Drake et al, U.S. Pat. No.3,313,185; Daggett, U.S. Pat. No. 3,616,711 and Brenner, U.S. Pat. No.3,766,806,

SUMMARY OF THE INVENTION

Briefly described the present invention comprises a circular saw bladeand a method and apparatus for automatically generating the same. Thecircular saw blade is characterized by a working surface whichsubstantially comprises a section of an elliptical cylinder. Accordingto the preferred embodiment of the invention the working surface islocated at the top of the front face of the tooth and has a negativerake angle in the range of -10° to -5° with reference to the rest of theface of the tooth. This geometry is especially useful with triple-chipcut saw blades of the sort frequently employed for cutting steel. Suchsteel cutting saw blades are typically provided with carbide tip insertswhich are adapted to take a special facing.

The improved working surface just described is imparted by a cup-shapedgrinding wheel having an abrasive rim. The grinding wheel is allowed topass over the face of the tooth at ay one of a variety of angles. Inpassing over the face of the tooth only one point or a plurality ofpoints lying in a straight line come in grinding contact with the toothat any one time. This technique will be referred to herein as pointcontact or edge grinding. Since the grinding wheel is circular andbecause it is generally tilted at an angle with respect to the tooth,the surface imparted to the tooth is elliptical. One major advantage ofthe improved method is that the wheel is self-dressing and thereforedoes not take on the contour of the tooth. According to the presentinvention, the cup-shaped grinding wheel comes into point contact withthe front face of the tooth as it passes over it. According to thetechnique described in the Von Arnauld/Murphy invention disclosed incopending application Ser. No. 540,449 now U.S. Pat. No. 3,964,349, thegrinding wheel would plunge into the surface of the tooth rather thanpass across it.

These and other features of the present invention will be more fullyunderstood in view of the following drawings and description of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1a is a side elevation of a conventional circular saw manufacturedaccording to the well known triple-chip form.

FIG. 1b is a superimposed front elevation of a high and low circular sawtooth which was fabricated in the triple-chip manner illustrated in FIG.1a.

FIG. 2a is a side elevation of the circular saw teeth disclosed in U.S.Pat. No. 3,576,061.

FIG. 2b is a front elevation of the tooth identified as element A inFIG. 2a.

FIG. 2c is a front elevation of the tooth identified as element B inFIG. 2a.

FIG. 3a is a side elevation of a section of a circular saw according toa prior art embodiment.

FIG. 3b is a top plan view of the prior art saw tooth of FIG. 3a.

FIG. 3c is a front superimposed view of the prior art saw tooth of FIG.3a.

FIG. 3d is a detailed view of prior art tooth B of FIG. 3a.

FIG. 3e is a view of the prior art tooth of FIG. 3d as seen fromperspective 3e 13 33.

FIG. 3f is a view of the prior art tooth of FIG. 3d as seen fromperspective 3f -- 3f.

FIG. 4 discloses the prior art technique of plunge grinding wherebycylindrical or conical surfaces are generated upon the teeth of acircular saw.

FIGS. 5a through 5e illustrate the method of point or end grinding theteeth of a circular saw according to a preferred embodiment of thepresent invention.

FIGS. 6a through 6c illustrate the saw teeth of the present invention asground according to the method illustrated in FIGS. 5a through 5e.

DESCRIPTION OF THE INVENTION

During the course of this detailed description like numbers will be usedto identify like elements according to the different figures illustratedherein.

FIGS. 1a through 4 illustrate relevant circular saw blade teethgenerated by various different prior art techniques. A similar completedescription of prior art techniques can be found in my copendingapplication U.S. Ser. No. 587,504 filed June 16, 1975 now U.S. Pat. No.4,012,820. That application discloses the structure of a circular sawblade having teeth with a continuously curved working or cuttingsurface. That structure will be referred to hereinafter as the Nowakstructure.

A prior art circular saw ground according to the well known triple-chiptechnique is illustrated in close-up detail in FIG. 1a. According to thetriple-chip technique a leading tooth A removes a center chip and atrailing tooth B removes two chips flanking the center chip removed bytooth A. The leading tooth A is typically taller than trailing tooth B.This relationship is illustrated in superimposed fashion in FIG. 1b. Theshape of the saw teeth can further be described in terms of a rake angleR and a clearance angle C. The rake angle R may be defined as the anglesubtended by the face of each tooth with respect to a line drawn betweenthe top of the tooth and passing through the geometrical center of acircular saw. The clearance angle C may be defined as the anglesubtended by a line parallel to the surface of the top of a tooth withrespect to a line tangent to the top of a tooth. The term rake angle andclearance angle as they are used in this context carry with themconventional connotations typically ascribed to them in the saw toothart.

FIGS. 2a through 2c illustrate another prior art triple-chip saw blade.The teeth disclosed in FIGS. 2a - c are described in further detail inthe Pahlitzsch patents U.S. Pat. Nos. 3,576,061 and 3,619,880. Amongother features, the "low" teeth of the Pahlitzsch invention includelaterally opposed cutting corners 30 and cutting edges 31 which add toits improved performance. The teeth described in FIGS. 2a through 2c arefrequently referred to in the saw tooth art as being teeth manufacturedaccording to the "German" geometry. Saw blades manufactured according tothe German geometry tend to exhibit better metal cutting characteristicsand longer life. However, they are uniformly difficult to grind sinceeach saw tooth requires at least two and sometimes more individualgrinding operations in order to produce the facets necessary to createthe desired geometry. It is a major purpose of the present invention toprovide circular saws having metal cutting characteristics superior tothe characteristics associated with the new German geometry and,further, it is the purpose of the present invention to provide ageometry which could be formed with only one grinding operation. Thedecrease in the number of grinding operations achieved by the presentinvention directly increases the profitability per grinding machine. Forexample, if a grinding machine in a saw blade grinding plant is beingused full time, and if the grinding steps per tooth can be reduced toone grinding operation, then that particular operation may be able togrind more saws for any given time period.

Prior art circular saw tooth generated according to the teaching of U.S.Pat. No. 4,012,820 are illustrated in detail in FIGS. 3a through 4. InFIG. 3a the saw teeth ground according to the prior art invention isillustrated in the context of a triple-chip ground saw blade. Accordingto the triple-chip principal, a plurality of high leading teeth A areinterspersed alternatively with a plurality of lower turning teeth B. Acircular saw ground according to this prior art teaching thereforeincludes a plurality of teeth A and B arranged in the following sequenceA, B, A, B, A, B, etc. Each tooth A and B includes a front leadingsurface 12 and a back trailing surface 14. Each tooth further includes apair of substantially similar side surfaces 16 and a front workingsurface 18. It will be noted in FIGS. 3a and 3b that the working surface18 appears on both the higher leading tooth A and the lower trailingtooth B. In FIG. 3c the front profile of the leading tooth A issuperimposed over the front profile of trailing tooth B. Since thecircular saw is manufactured using the triple-chip technique, theleading tooth A is higher than the trailing tooth B by an amount H. Hmay typically range from 0.010 to 0.012 inches. The leading tooth A alsoincludes a central top plateau surface P with dimensions ofapproximately 0.12 inches. The top sides of tooth A are tapered with abevel BV of approximately 45°. Both teeth have a side clearance SC ofapproximately 2° and tooth B exhibits a Kerf K of 0.247 inchesapproximately.

As shown in FIGS. 3a and 3b, both teeth A and B exhibit a tooth depth TDof approximately 0.18 inches and a tooth height TH of approximately 0.50inches. The tooth clearance angle C lies in the range of 9°-11°. Theworking surface 18 of tooth A and B has a height of WH of approximately1.2 inches and a width WD or crown of approximately 0.007 inches whenviewed from above as in FIG. 3b. According to FIG. 3a the un-groundleading surface 12 exhibits a forward rake angle R₁ of approximately15°. The working surface 18, however, exhibits a minus rake angle R₂ ofapproximately -10°. In practice the rake angle R₂ of the working surface18 can be anywhere within the range of -20° to +25°. It has been foundthough that for the majority of all operations, a negative rake angle R₂in the range of -5° to -10° is preferable.

The working surface 18 is generated by a grinding wheel 20 having anabrasive inner grinding surface or rim 22. The grinding method usingthat grinding which is hereinafter referred to as plunge grinding and isillustrated in FIG. 4. According to the plunge grinding technique, thegrinding wheel 20 is caused to revolve about a central axis AW. Thedistance from the grinding axis AW to the surface of the tooth andtherefore to the inner surface 24 of the abrasive rim 22 is designatedas RG. In practice, the grinding radius of the wheel RG may be in therange of 1 - 4 inches. The radius RG as illustrated in FIGS. 3a and 3dis approximately 1 inch. The working surface 18 imparted by the grindingwheel 20 to tooth A or B has a shape that is dictated largely by thecontour of the surface 24 of the tooth 22. For example, if the surface24 has a straight profile as shown in FIG. 4 but is tapered inwardtoward the axis AW, the working surface of the tooth 18 may be slightlyconical in shape. In other words, the working surface 18 will describe asection of a cone. If grinding surface 24 were irregular or curved, thenthe surface 18 generated by such a grinding surface 24 would be asection of an irregular surface of rotation. The characteristic that allworking surfaces 18 have a common is that they are all generated by acircular grinding wheel of the sort illustrated in FIG. 4. Therefore,the working surface 18 must be such than the center of the workingsurface 26 is slightly more forward than the sides of the workingsurface 28 where they come into contact with the side 16 of the teeth Aor B. The working surface 18 generated according to the method of FIG. 4can also be described in terms of a plane P which is perpendicular tothe reference angle AW and passes through the working surface 18. Sincethe working surface 18 is generated by the revolution of the wheel 20,points on its surface can be characterized by the fact that all pointson the working surface 18 which lie in the same given plane Pperpendicular to the axis of rotation of the grinding wheel AW areequally distant from any given point on that axis AW. This isself-evident since any given point X on the face of the grinding surface24 will revolve in a circle about the reference axis AW. Since theworking surface 18 is a section of a surface of rotation, that sectionof the working surface 18 cut by the plane P will be equally distantfrom any given point on reference axis AW.

Details of a typical tooth generated by the prior art plunge grindingtechnique are shown in FIGS. 3d, 3e and ef. FIGS. 3d - 3f illustrate, inparticular, the curved nature of the working surface 18. As describedpreviously, the center 26 of the working surface 18 is further advancedthan the edges of the working surface 28. This feature is especiallyprominent in FIG. 3f. FIG. 3f corresponds to a view of the workingsurface 18 wherein the plane of 3f is parallel to plane P as illustratedin FIG. 4. Note that the working surface 18 as seen from view 3f forms asector of a circle having a radius corresponding to the grinding radiusRD of the grinding wheel 20. According to the preferred embodiment ofthe invention, the working surface 18 may actually form a section of thearea of a cone. However, since the working surface 18 is produced byrotary action, any plane perpendicular to the axis of rotation AW of thegrinding wheel 20 and passing through the working surface 18 will bisecta section of a circle. Therefore, any point on that bisected portion ofthe working section 18 will be equally distant from any given point onthe grinding axis AW. This relationship will be so regardless of whetherthe working surface 18 is a portion of a cone, a cylinder or somesurface exhibiting irregularities in the direction of the reference axisAW.

The plunge grinding method of producing saw teeth having a conical orcylindrical geometry was discussed with reference to FIG. 4. In FIG. 4the grinding wheel 20 includes an abrasive inner rim 22 having agrinding surface 24 which is canted at an angle with respect toreference axis AW. According to this plunge grinding technique, thegrinding wheel 20 is brought into grinding contact with the blade 10 insuch a manner that the axis AW almost passes through the center of thecircular saw 10. Unfortunately, this technique is rather limited sinceit only produces a saw tooth having a fixed rake angle corresponding tothe angle between the grinding surface 24 and the axis AW. Since theaxis AW is unchangeable relative to the rest of the machinery, a newgrinding wheel 20 must be employed each time a saw is to be ground to adifferent rake angle.

One technique employed in the prior art to overcome the necessity ofhaving multiple grinding wheels for different rake angle requirementsdescribed in U.S. Pat. No. 4,012,820 and is illustrated therein as FIG.4b. According to that technique, the grinding surface 24 of the abrasivegrinding rim 22 is approximately parallel to the reference axis AW ofthe grinding wheel 20. In order to achieve different rake angles, thegrinding wheel 20 is set on a spindle (not illustrated) which may beselectively positioned at a variety of different angles relative to thecircular saw blade 10. By adjusting the reference axis AW relative tothe saw blade 10 it is possible to generate a variety of workingsurfaces 18 having different rake angles. The aforedescribed techniqueis identical in some respects to the technique further described herein.

An understanding of the foregoing prior art is essential to a completeunderstanding of the present invention. For that reason, the prior arthas been explained in great detail. In particular, the plunge grindingtechnique has been thoroughly discussed because the present inventioncomprises a distinct improvement over that prior art method. Inaddition, the teeth of the circular saw generated by the method of thepresent invention are very similar to the prior art teeth illustrated inFIGS. 3a through 3f except for the fact that the teeth of the presentinvention have a working surface whose contour comprises a section of anelliptical cylinder rather than a section of a cone or sphericalcylinder. These details will be discussed further with reference toFIGS. 6a through 6c.

There are several specific disadvantages to the plunge grindingtechnique illustrated in FIG. 4. One disadvantage is that a variety ofgrinding wheels with different degrees of curvature are necessary toproduce a variety of different working surfaces. Second, since thegrinding wheel according to the prior art technique typically plunges tothe same depth each time, it has been found that the abrasive inner rimwill wear unevenly. Uneven wear of the abrasive inner rim will in turncause progressively irregular grindings of the working surface. Third,when using the plunge grinding technique, it was often found necessaryto make the diameter of the wheel slightly oversized so as to avoidcontacting the circular saw at more than one point. Fourth thesequencing means necessary to control the relative motion of the machineelements was moderately complicated. And, fifth, despite the fact thatthe plunge grinding technique saved a lot of time it was determined thatexcess time was spent in the retracting and advancing of the grindingwheel.

The method of point (i.e. edge) grinding the tooth of a circular sawblade according to the present invention is illustrated in FIGS. 5athrough 5e. In FIG. 5a the grinding wheel 32 is illustrated at thebeginning of the machine cycle in its fully retracted position. Thedistance between the grinding wheel 32 and the saw blade 34 isexaggerated for purposes of illustration only. The grinding wheel 32includes an abrasive rim 36 having a leading edge 38. The saw blade 34is equipped with a plurality of carbide inserts 40 in the same manner asdescribed with reference to the prior art in FIGS. 1 through 3f. Fromthe fully retracted position as shown in FIG. 5a the wheel 32 is nextadvanced in the direction of arrow 42 as shown in FIG. 5b. In FIG. 5bthe leading edge 38 of abrasive rim 36 is just making contact with thetip 44 of carbide insert 40. As shown in FIG. 5c, the leading edge 38continues across the top face of the saw tooth and while it does itimparts an elliptical working surface 46 to the carbide insert 40. Afterthe cup-shaped grinding wheel 32 has passed over insert 40 it isthereafter retracted in the direction of arrow 48 and reassumes thefully retracted position as shown in FIG. 5a. Finally, the next toothillustrated as element 50 is indexed forward in the direction of arrow52 and assumes the position previously occupied by insert 40 as shown inFIG. 5a. At that point the sequence illustrated in FIGS. 5a to 5e isrepeated until all of the teeth of the circular saw have been ground.

The terms point or edge grinding may be used interchangeably to describethe method illustrated in FIGS. 5a through 5e. The essence of the methodis that only the leading edge 38 makes contact with carbide insert 40.This technique is clearly distinguishable from plunge grinding in twomajor respects. First of all, only a very small portion of the grindingsurface 38 contacts the carbide insert 40. Secondly, the point ofcontact of the leading edge passes over the face of the tooth as thetooth is ground. According to the prior art plunge grinding techniquethe abrasive inner rim of the grinding wheel is pushed into the face ofthe tooth rather than across it. several major advantages over the priorart plunge grinding technique. First of all, it is possible to grind avariety of working surfaces on a carbide tooth with the same cup-shapedgrinding wheel. This is accomplished by tilting the angle of attack ofthe grinding wheel with respect to the circular saw. The grinding wheelimparts a section of an elliptical cylinder to the working surface sincethe projection of a tilted circle against a plane is an ellipse. Anotheradvantage to the present technique is that a much shorter retracting andadvancing stroke is required due to the relative geometry of thegrinding wheel 32 with respect to the saw blade 34. One of the mostimportant advantages of the technique described in FIGS. 5a through 5eis that the grinding wheel is self-dressing and therefore does notassume the irregularities of the saw blade tooth in the mannerfrequently associated with plunge grinding. The term self-dressing isused to suggest that the abrasive rim 36 does not have to be removedfrom time to time and reground or otherwise redressed. Accordingly, thecup-shaped grinding wheel is used until such time as the grinding rim 36has been entirely worn down at which point it is removed and the entireassembly is replaced by a new grinding wheel. Due to the limitations ofthe plunge grinding technique, it has been necessary to remove thecup-shaped grinding wheel illustrated in FIG. 4 frequently so that theabrasive inner rim may be redressed.

If the self-dressing grinding wheel 32 is continually used the leadingedge 38 of the abrasive rim 36 will start to wear. Under thosecircumstances the leading edge 38 will start to move backwards therebyrounding the corner of the abrasive rim 36. However, while this happensit is important to keep in mind that there is still only point or edgecontact between the abrasive inner rim and the carbide insert 40. As theleading edge wears down the locus of contacting edges moves slowlybackward imparting a rounded profile to the abrasive rim 36. It may bedesirable for the machine operator to adjust the position of thegrinding wheel 32 from time to time so as to maximize the efficiency ofthe grinding operation. The edge grinding technique just described hasthe major advantage that the grinding wheel does not have to be removedperiodically and redressed. Instead, by using the edge grindingtechnique the same grinding wheel may be used continually until theabrasive rim is entirely worn away at which point the grinding wheel isreplaced by a new one.

One tooth ground according to the edge grinding technique described inFIGS. 5a through 5e is illustrated in different views in FIGS. 6athrough 6c respectively. For ease of illustration only one tooth 40 ofthe circular saw 34 is illustrated. That one tooth could be either a"high" tooth of a triple-chip cut circular saw blade. The same tooth isseen in FIG. 6b from the front. It is clear from FIGS. 6a and 6b thatthe carbide insert is identical to that of the prior art such asillustrated in FIG. 3e except for the characteristics of the workingsurface. The improved geometry of the working surface 46 will beappreciated with reference to FIG. 6c when compared to the prior art asillustrated in FIG. 3f. From perspective 6c--6c it is clear that theworking surface 46 has a contour which comprises a portion of an ellipse54. Since working surface 46 actually lies in a three dimensional plane,it is clear therefore that working surface 46 actually comprises aportion of an elliptical cylinder. Ellipse 54 is the projection of thegrinding wheel upon the carbide insert tooth 40. If there is a zeroangle of attack then the ellipse forms a circle. If the angle of attackis other than zero, then the curve 54 becomes more elliptical. As withall ellipses the figure has two focii f₁ and f₂. The major axis 56 ofthe ellipse is defined as the distance from the center of the ellipse toeither one of the two focci f₁ or f₂. The minor axis 58 is defined asthe distance from the center of the ellipse to the closest portion ofthe curve. It will be noted from FIG. 6c that the working surface 46comprises that portion of the ellipse 54 which is closest to the center60. In other words, the contour of the working surface 46 is taken fromthe longest side of the ellipse 54 and includes the point from which theminor axis 58 is measured with respect to the center 60 of the ellipse.It has been found that this portion of the ellipse exhibits the bestcutting characteristics and is easiest to grind.

As stated above, the circular saw 34 is identical to those described inFIGS. 3a through 3f except for the nature of the working surface 46.Therefore, the saw tooth according to the preferred embodimentillustrated in FIGS. 6a through 6c also exhibits the followingcharacteristics: A tooth depth TD of approximately 0.18 inch and a toothheight TH of approximately 0.50 inch; a tooth clearance angle C in therange of 9°-11°; a working surface 46 with a height WH of approximately0.12 inch and a width WD or crown of approximately 0.007 inch when seenfrom perspective 6b -- 6b; a forward rake angle R₁ of approximately 15°;a negative rake angle on the working surface 46 of approximately -10°.In practice, the rake angle R₂ of the working surface 46 can be anywherewithin the range of -20° to +25°.It has been found though that with themajority of all operations, a negative rake angle R₂ in the range of -5°to -10° is preferable. In addition to the foregoing characteristics theprior art teeth and the teeth according to the preferred embodiment ofthe present invention also exhibit the same following proportions: Theleading and trailing teeth may vary in height H in the range from 0.010to 0.012; the leading teeth and subsequent teeth would have a centraltop plateau surface P with dimensions of approximately 0.12; the topsides of the teeth are tapered with a bevel BV of approximately 45°;allteeth would have a side clearance SC of approximately 2° and the teethwould exhibit a kerf K of approximately 0.247 inches. The foregoing arethe general characteristics of a tooth according to the preferredembodiment of the present invention as adapted for use with atriple-chip steel cutting circular saw blade with carbide inserts.

Certain modifications of the invention just described are considered tobe within the scope and spirit of the invention. For example, a varietyof abrasive grinding wheel rims can be satisfactorily employed toproduce the results described. The preferred saw blade described is onehaving carbide inserts and adapted to cut steel stock and the like. Itwill be appreciated by those of ordinary skill in the art, however, thatother types of saws may be produced according to these teachings.

While the present invention has been described with reference to thepreferred embodiment thereof, it will be appreciated by those ofordinary skill in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention.

We claim:
 1. A circular saw having teeth with an improved metal cuttinggeometry comprising:a circular saw blade body; and, a plurality of sawteeth means attached to said saw blade body and separated one fromanother by gullet means, said saw teeth means including a plurality ofhigher and lower teeth arranged in a triple-chip like manner, said teethmeans including at least a leading face and a first and a second sideface, said saw teeth means further including a continuously curvedcutting surface located on the upper portion of said leading face ofsaid saw teeth means, said continuously curved cutting surface havingtwo edge portions where said continuously curved cutting surface meetssaid first and second side faces and a central portion intermediate saidtwo edge portions and advanced forward of said two edge portions, saidcutting surface having a substantially eliptical cross-section.
 2. Thecircular saw of claim 1 wherein said cutting surface has a rake angle inthe range of -10° to -5°.
 3. The circular saw of claim 1 wherein saidteeth means further include a top surface.
 4. The circular saw of claim3 wherein said cutting surface abuts said top surface.
 5. The circularsaw of claim 1 wherein the cutting surface has a rake angle in the rangeof -20° to +25°.
 6. The circular saw of claim 5 wherein the cuttingsurface has a rake angle in the range of -10° to -5°.